This invention relates to a method and apparatus for calibrating a height control system of a vehicle. Such height control systems generally comprise an adjusting device for the height h of the body of the vehicle with respect to the chassis or a road surface, as well as a control device for the adjusting device which is in turn controlled by a control apparatus, and a relative-height sensor which detects the height of the vehicle body relative to a predetermined reference point. The adjusting device may, for example, be a hydraulic or pneumatic cylinder arranged in a spring strut which supports the chassis with respect to the body. The control device, in addition to a pressure supply circuit having a pump, a sump and a pressure accumulator, also has control elements (solenoid valves) by means of which the pressure in the hydraulic cylinders of individual wheels or axles may be increased (to lift the vehicle) or may be reduced (to lower the vehicle). This type of a height control system is known, and is illustrated for example, by U.S. Pat. No. 4,593,920. Comparable systems are also shown in the German patent document DE-C2 34 37 799, and in U.S. Pat. Nos. 4,659,104, and 4,700,303.
However, tolerances that occur in the production and the assembly of the vehicle can result in an erroneous actual height signal (hi) emitted by the relative-height sensor, and may thus result in an inaccurate height control.
It is therefore an object of the present invention to provide a method and apparatus for the calibration of a height control system of a vehicle which permits compensation for these tolerances by simple means.
This and other objects are achieved by providing an interface between the vehicle height control system and a diagnostic device which initiates a series of calibration steps in which the control system is commanded to bring the vehicle to a predetermined height, the actual height of the vehicle is then measured by external means and compared with the predetermined height, and the control system is adjusted to compensate for any deviation between the actual vehicle height and the predetermined height.
Principal advantages of the present invention are that it provides a simple means to compensate for tolerances caused by the production and the assembly process, particularly at the vehicle body, the connection of the wheel suspension to the body, the chassis itself and at the relative-height sensor, without any extensive and expensive mechanical balancing operations that might, for example, be carried out at the sensor itself, its connection to the vehicle body or at a balancing device (control potentiometer) at the control apparatus.
The control apparatus is capable of carrying out diagnostic operations of the height control system in a manner that is known per se. (See, for example, German patent documents DE-A1 37 26 344, DE-A1 35 40 599 and DE-A1 34 32 430.) The calibration process is carried out a diagnostic mode into which the control apparatus is brought by means of the connection of a diagnostic apparatus, such as Bosch Model KTS 301, or a correspondingly configured personal computer.
The "height adjustment" mode is initiated by the diagnostic apparatus and the height of the body of the vehicle is measured relative to a scale, or by other means of a normal measurement. By way of input devices at the diagnostic apparatus, the control devices are controlled in increments until the height (h) corresponds to the preset height (hsns) (normal position). Thereafter, in a set mode initiated by the diagnostic apparatus, the actual values (hi) of the relative-height sensors are substituted as the desired values (hsn) for the normal position, and the adjusting (and the diagnostic analysis) are stopped.
Other objects, advantages and novel features of the present intention will become apparent from the following detailed description of the invention when considered in conjunction with the following drawings: